Increasing the efficiency of power generation plants is in progress in response to demands for reduction of carbon dioxide, resource saving, and the like. Specifically, increasing the temperature of a working fluid of a gas turbine and a steam turbine, employing a combined cycle and the like are actively in progress. Further, research and development of collection techniques of carbon dioxide are in progress.
FIG. 6 is a system diagram of a conventional gas turbine facility 300 in which a part of carbon dioxide produced in a combustor is circulated as a working fluid. FIG. 7 is a view schematically illustrating a vertical section of a combustor 313 provided in the conventional gas turbine facility 300.
As illustrated in FIG. 6, in the conventional gas turbine facility 300, oxygen separated by an air separating apparatus (not illustrated) is introduced to a pipe 340. Then, the oxygen is pressurized by a compressor 310 and its flow rate is controlled by a flow rate regulating valve 311. The oxygen having passed through the flow rate regulating valve 311 is heated by receiving a heat quantity from a later-described combustion gas in a heat exchanger 312 and supplied to the combustor 313.
A fuel is guided to a pipe 341 from a fuel supply source (not illustrated). Then, the fuel has its flow rate regulated by a flow rate regulating valve 314 and is supplied to the combustor 313. This fuel is hydrocarbon.
In the combustor 313, as illustrated in FIG. 7, the oxygen supplied from the pipe 340 and the fuel supplied from the pipe 341 are introduced to a combustion region. Then, the oxygen and the fuel undergo a combustion reaction to produce the combustion gas. The combustion gas contains carbon dioxide and water vapor. The flow rates of the fuel and the oxygen are regulated so as to have a stoichiometric mixture ratio (theoretical mixture ratio) in a state where they are completely mixed together.
The combustion gas produced in the combustor 313 is introduced to a turbine 315. Note that, as illustrated in FIG. 6, for example, a power generator 319 is coupled to the turbine 315. The combustion gas having performed expansion work in the turbine 315 passes through the heat exchanger 312. At this time, the heat quantity is released to heat the above-described oxygen flowing through the pipe 340 and later-described carbon dioxide flowing through a pipe 343. The combustion gas having passed through the heat exchanger 312 passes through a heat exchanger 316 further. When the combustion gas passes through the heat exchanger 316, the water vapor in the combustion gas condenses into water. The water is discharged through a pipe 342 to the outside.
The carbon dioxide separated from the water vapor is pressurized by a compressor 317 interposed in the pipe 343 to become a supercritical fluid. A part of the pressurized carbon dioxide is introduced to a pipe 344 branching off from the pipe 343. The carbon dioxide introduced to the pipe 344 has its flow rate regulated by a flow rate regulating valve 318 and is extracted to the outside.
Meanwhile, the remaining part of the carbon dioxide flows through the pipe 343. Then, the carbon dioxide is heated in the heat exchanger 312 and, as illustrated in FIG. 7, is supplied into a combustor casing 350 housing the combustor 313. A temperature of the carbon dioxide having passed through the heat exchanger 312 becomes about 700° C. Here, the combustor casing 350 is constituted by an upstream-side casing 351a and a downstream-side casing 351b. 
The carbon dioxide guided into the upstream-side casing 351a flows toward the turbine 315 between the downstream-side casing 351b and, a combustor liner 352 and a transition piece 353 (tail pipe). Thus, the carbon dioxide other than the one exhausted from the pipe 344 circulates in the system.
When the carbon dioxide flows between the downstream-side casing 351b and, the combustor liner 352 and the transition piece 353, the carbon dioxide cools the combustor liner 352 and the transition piece 353. The above cooling is performed by porous film cooling and the like, for example. A part of the carbon dioxide is introduced into the combustor liner 352 and the transition piece 353 from holes 354, 356 of a porous film cooling part, dilution holes 355, and the like, as illustrated in FIG. 7. Further, this carbon dioxide is used also for cooling stationary blades 360 and rotor blades 361 of the turbine 315.
The carbon dioxide introduced into the combustor liner 352 and the transition piece 353 is introduced to the turbine 315 together with the combustion gas produced by combustion.
Here, the upstream-side casing 351a and the downstream-side casing 351b are exposed to the high-temperature carbon dioxide, and therefore, they are composed of an expensive Ni-based alloy.
As described above, in the conventional gas turbine facility 300, the upstream-side casing 351a and the downstream-side casing 351b which are exposed to the high-temperature carbon dioxide are to be composed of the expensive Ni-based alloy. Therefore, a manufacturing cost for the gas turbine facility increases.